add google photos support & fix preview

README.md

@@ -5,7 +5,8 @@
 > fixed and replied by human.
 
 A Fabric client mod that sends your Minecraft screenshots to [Immich](https://immich.app)
-and lets you browse the album back inside the game. This mod also supports periodic screenshooting.
+or [Google Photos](https://photos.google.com) and lets you browse the album back
+inside the game. This mod also supports periodic screenshooting.
 
 Take a screenshot with F2 and it uploads in the background. Press F6 to see what
 is uploading, scroll through the album's timeline, or change how any of it
@@ -73,6 +74,49 @@ clients or worlds stays tellable apart.
 Settings save when you close the screen. **Revert** undoes everything since you
 opened it.
 
+## Connect it to Google Photos
+
+Press **F6** → **Settings** and switch **Provider** to Google Photos. The two
+fields are an **OAuth client ID** and an **OAuth client secret**, and you have to
+make them yourself — there is no key to paste from a Google Photos settings page,
+and this mod cannot ship one for you. Google classes the Photos scopes as
+restricted, so a shipped credential would need Google's verification, would name
+this mod as the data controller for everyone's photos, and would break for
+everybody at once the day it was revoked.
+
+Making one is a five-minute detour through the
+[Google Cloud console](https://console.cloud.google.com), once:
+
+1. Create a project (any name).
+2. **APIs & Services → Library**, find **Photos Library API**, press Enable.
+3. **APIs & Services → OAuth consent screen**: pick External, fill in the three
+   required fields, and add your own Google address under **Test users**. The app
+   can stay unpublished — a test user is exactly what you are.
+4. **APIs & Services → Credentials → Create credentials → OAuth client ID**,
+   application type **Desktop app**. Copy the client ID and client secret.
+
+Paste both into Settings and press **Test**. Your browser opens Google's consent
+page, you allow it, and the tab tells you to go back to the game; the settings
+screen then shows the account you signed in as. Nothing is typed into Minecraft
+except the two client fields, and the sign-in that comes back is kept in
+`google-photos.json` next to your settings, readable only by your user account.
+
+Three things are genuinely different from Immich, and all three are Google's
+rules rather than choices made here:
+
+- **Browse only shows what PhotoSync uploaded.** Google withdrew the broad
+  library scopes in March 2025. No application can read your Google Photos
+  account any more, so the Browse tab is a view of this mod's own screenshots —
+  not of your holiday photos.
+- **Albums have to be ones PhotoSync made.** The album picker lists those only,
+  because an upload into any other album is refused. Type a name and press Create
+  and it will be there.
+- **Retries can leave a duplicate.** The Library API has no checksum, no
+  duplicate response, and no way to ask whether something is already stored. If
+  the game dies between an upload finishing and its confirmation arriving, the
+  retry stores a second copy. Immich does not have this problem; Google's API
+  gives nothing to solve it with.
+
 ## The screens
 
 **Uploads** is the queue: everything still in flight plus the last hundred that
@@ -148,7 +192,7 @@ Either way nothing is lost. The queue is on disk and is written through on every
 state change, so unfinished uploads resume the next time you play — the dialog
 exists to save you the wait, not to prevent a loss. An upload that was mid-flight
 when the game died is simply tried again, and Immich recognises the retry as a
-duplicate rather than storing a second copy.
+duplicate rather than storing a second copy. (Google Photos cannot; see above.)
 
 You can turn the dialog off under Settings → Uploads → *Ask before quitting
 mid-upload*, in which case the game gets a three-second grace period to finish
@@ -232,10 +276,12 @@ the way it is, [`docs/PORTING.md`](docs/PORTING.md) is the document for that: it
 covers the bucket scheme, the measured API breakpoints between every supported
 version, and the procedure for a new release.
 
-Adding a photo service other than Immich means implementing `PhotoProvider` and
+Adding a third photo service means implementing `PhotoProvider` and
 `ProviderFactory` in `shared/core` and registering it with `ProviderCatalog`. No
 UI or platform code needs to change — the settings screen builds its connection
-fields from what the provider declares.
+fields from what the provider declares. `provider/immich` is the simpler of the
+two worked examples; `provider/google` is the one to read if the service needs
+OAuth rather than a key.
 
 ## Licence